The present invention generally relates to a scanning unit, and more particularly, to a scanning unit for a magnetic position measuring device.
Magnetic position measuring devices usually include a magnetic measuring graduation that includes alternately arranged subareas having different magnetisation intensities and a scanning unit movable relative thereto in the direction of measurement. A detector unit, among other things, having suitable magnetically sensitive detector elements is provided on the sides of the scanning unit. Thin layers made of a magneto-resistive material are often used as detector elements, which however are extremely sensitive to mechanical influences. Therefore, if a magnetic position measuring device having such a scanning unit is used in a machine tool, the detector elements, i.e., the detector unit, may become damaged by coolants, chips, etc. during the measuring operation. This in turn would result in failure of the position measuring device.
In order to prevent damage, it is known in such a position measuring device that a detector unit arranged in a recess of a carrier element can be protected with a covering element arranged over it. If a thin metal foil is provided as the covering element, it is, however, relatively difficult to arrange this foil to be exactly flat in this area. However, if the metal foil is not exactly flat, the distance between the detector elements and the measuring graduation will vary for a given scanning distance between the measuring graduation and the covering element. Due to the sensitive dependence of the detector signals on this distance, undesirably fluctuating signal amplitudes may result. Furthermore, a not exactly flat arrangement of the metal foil may result in metal chips or other impurities becoming wedged at this point between the measuring graduation and the scanning unit.
An object of the present invention is therefore to provide a scanning unit, in particular for magnetic position measuring devices, whose detector unit is reliably secured against mechanical influences.
The scanning unit according to an embodiment of the present invention offers a series of advantages compared to previous devices. Thus, a stable and compact design of the overall scanning unit results due to the filling material provided inside the recess. Furthermore, the measures according to the present invention allow an extremely accurate flat arrangement of a metal foil to be provided as the covering element, which protects the detector unit against mechanical influences. This in turn results in the desired insensitivity to deposition of contaminants, as well as in stable, low-noise scanning signals.
Furthermore, if the detector unit is contacted using flexible printed conductors, a relatively simple, easy to automate contacting can be implemented.
If also the hole through which the connecting leads are run is filled with the filling material, the electric connecting leads in the scanning unit are also reliably protected against mechanical damage.
Due to the use of a filling material in the recess in the scanning unit according to an embodiment of the present invention, which contracts, i.e., shrinks, as it sets, when a metal foil is used as a covering element it adapts itself to the contour of the detector elements and the support elements. This results in a rigid support of the metal foil which prevents any failure of the adhesive bond between the foil and the support element. Furthermore, the shrinkage of the filling material ensures that only thrust and pressure stresses occur in the flat adhesive surfaces, which reliably prevents the metal foil from peeling off.
As an additional advantage of the use of a suitable filling material, the creep distances for impurities are increased, should the metal foil be mechanically damaged, for example.
According to embodiments of the present invention, scanning units based on other physical scanning principles, for example, optical, inductive, or capacitive systems, can also be formed in a position measuring device. Instead of the magnetically sensitive detector elements, corresponding alternative detector elements could then be provided. In addition, in the case of an optical position measuring device, the covering element may be designed to be transparent.
The scanning unit designed according to an embodiment of the present invention can be used in both linear and rotational position measuring devices. In one embodiment, the invention is a scanning unit for a magnetic position measuring device that includes a carrier body having at least one recess and at least one bore hole, the bore hole being in communication with the recess, detector unit, arranged in the recess, having at least one electrical connecting lead disposed through the bore hole, a covering element adapted to cover the recess, and a filling material adapted to fill a remaining area of the recess under the covering element.
In a different embodiment, the invention is a scanning unit for a magnetic position measuring device, comprising a carrier body having at least one recess and at least one bore hole, the bore hole being in communication with the recess, a detector unit, arranged in the recess, having at least one electrical connecting lead disposed through the bore hole, and a covering element adapted to cover the recess. The invention also includes a filling material adapted to fill a remaining area of the recess under the covering element and at least one support element arranged in the area of the recess and adapted to support the covering element. The invention can also include at least one assembly stop being arranged in said recess for accurate positioning of said detector unit.